Method and tooling for forming a stent and stent so formed

ABSTRACT

The present invention relates to a method and tooling for forming a stent and the stent so formed. The stent includes filaments of a first material and joints of a second material. The present invention also discloses the above described stent in combination with an angioplasty balloon. The tooling in accordance with the present invention provides a fixture having grooves that receive the filaments of the stent to hold the filaments in place for joining. The joining of all of the filaments can be performed simultaneously by laser welding or injection molding a joint material. The tooling in accordance with the present invention also provides the capability to mold the stent as one piece. The method in accordance with the present invention includes the steps of providing a fixture with internal grooves, placing filaments into the grooves and joining the filaments together. The method also includes providing a mold having internal grooves, and injecting a molten material into the mold to fill the grooves so as to create a one-piece stent of polymer and/or metallic materials.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention, generally, relates to endoprosthesis, andmore particularly, it relates to a new stent, a stent in combinationwith an angioplasty balloon, tooling for forming a stent, and a methodof fabricating a stent.

[0003] 2. Related Art

[0004] Stents are devices used to support the walls of weak arteries andare particularly useful in the medical field of angioplasty involvingthe reconstruction of vessels that carry blood in both humans andanimals. The stent is used to maintain such blood vessels, structurally,in a clear and open condition. Most arterial stents are formed from thinwire, e.g., 0.005 inch diameter wire. Stents are often made from inertmetals such as stainless steel or tantalum. However, plastic stents areavailable and provide more flexibility. Unfortunately, plastic stentsalso lack sufficient radial stiffness for artery wall support.

[0005] For a stent to achieve maximum usefulness, it must be flexible ina bending mode during insertion, and it must exhibit stiffness in bothtorsional and cylindrical modes in order to provide support. The stentstoday are formed into the required configuration to permit a high levelof plastic deformation to be achieved during their use. During use, anangioplasty balloon may be inserted into a stent which is thenplastically compressed around the balloon. This assembly is insertedinto a patient's blood vessel, usually an artery, and moved intoposition. The balloon is inflated to enlarge the stent to a desireddiameter, after which the balloon is removed.

[0006] The stent, within an artery, or within any other type of vessel,is exposed to repetitive flexing as a part of a circulatory system, bothfrom the systolic and the diastolic variations in blood pressure andfrom variations in movement of a body.

[0007] One method of stent fabrication today continuously feeds a wirefrom a spool to be formed into a generally sinusoidal configuration.Then, the wire in this sinusoidal configuration is wound around amandrel in order to produce a helical arrangement. Next, the crests andtroughs in the helical arrangement are aligned so that they touch atpoints, and then crests and troughs are welded at the points to providethe required supporting structure. The above described steps, however,in conjunction with the heating and cooling encountered during welding,create an undesirable work-hardening in the wire. This work hardeninglowers much of the wire's ability to provide support in use.Additionally, loading and unloading of a metallic stent during useproduces further fatigue of the metal, causing premature failure ofsupport.

[0008] An additional disadvantage of present fabrication methods is thatthe deformation of the wire into a desired position is also relativelyimprecise such that a uniformly shaped stent is difficult to create.Further, since each joint is welded individually, inconsistency ofstructure can be created. As a result, the stents so fabricated alsolack in consistency of torsional and radial stiffness. The need todeform the wire into a given position and then join the wire alsoinvolves very high costs.

[0009] Examples of related art, which are hereby incorporated byreference, are:

[0010] U.S. Pat. No. 5,370,683 to Fontaine and assigned to Cook, Inc.describes a stent formed of a single filament wrapped around a mandrelwith a series of U-shaped bends.

[0011] U.S. Pat. No. 5,304,200 to Spaulding and assigned to Cordis Corp.describes a method of making stents involving winding an elongatedstrand forming a helix like structure with the ends welded to anadjacent section.

[0012] U.S. Pat. No. 5,217,483 to Tower and assigned to Numed, Inc.describes a stent arranged to have U-shaped sections formed in acontinuous wire with two ends and with the ends attached together toprevent axial expansion.

[0013] U.S. Pat. No. 5,549,663 to Cottone, Jr. and assigned to CordisCorp. describes a stent formed by wrapping a wire around a mandrel andjoining the filaments by welding.

[0014] U.S. Pat. No. 5,629,077 to Turulund et al. and assigned toAdvanced Cardiovascular Systems, Inc. describes a stent made completelyof biodegradable material.

[0015] U.S. Pat. No. 5,630,829 to Lauterjung and assigned toInterVascular, Inc. describes a stent in which adjacent stents may beconnected to one another by welding at least one opposed pair of cuspstogether.

[0016] Accordingly, there is a need for a stent which consistentlyexhibits flexibility during insertion, and stiffness with a high levelof plastic deformation in both torsional and radial modes to providesupport during use. Further, there is a need for a stent fabricationprocess and tooling which creates the above described stent more easilythan conventional methods and without the problem of work hardening andhigh cost.

SUMMARY OF THE INVENTION

[0017] The present invention is a method and tooling for forming a stentand the stent so formed. In one general aspect in accordance with thepresent invention is provided a stent including at least one filamentmade of a first material, and joints made of a second materialconnecting selected filaments to one another. This aspect allows forconsistent flexibility during insertion, stiffness and a high level ofplastic deformation to provide support during use. The present inventionalso includes the above described stent in combination with anangioplasty balloon.

[0018] In a second general aspect in accordance with the presentinvention is provided tooling for forming a stent comprising a firstpart having grooves for aligning the filaments of the stent to hold thefilaments in place for joining. In a third general aspect of the presentinvention is provided tooling for forming a stent including a device forpositioning filaments and a device for joining filaments. The above twoaspects allow the joining of all of the filaments to be performedsimultaneously by laser welding or injection molding a joint materialsuch as a polymer or metal. As a result, repetitive welds anddeformations are alleviated, the manufacturing process is quicker, andjoints of the stent are more consistently aligned. The tooling inaccordance with the present invention also provides the capability tomold the stent as one piece.

[0019] In a fourth general aspect in accordance with the presentinvention is provided a method that eliminates repetitive welds andbending by: providing a fixture with internal grooves, placing filamentsinto the grooves and joining the filaments together. The method reducesthe repetitive bending and welding of the related art devices. Further,the method provides enhanced alignment of joints of the filamentmaterial, eliminates the need for time consuming inspection of jointsthrough injection molding, and quickens the manufacturing process.

[0020] The foregoing and other features and advantages of the inventionwill be apparent from the following more particular description ofpreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The preferred embodiments of this invention will be described indetail, with reference to the following figures, wherein likedesignations denote like elements, and wherein:

[0022]FIG. 1 shows an isometric view of a stent in accordance with afirst embodiment of the present invention;

[0023]FIG. 2 shows an isometric view of a stent in accordance with asecond embodiment of the present invention;

[0024]FIGS. 3 and 3B show an isometric and enlarged view of a mold inaccordance with a first embodiment of the present invention;

[0025]FIG. 3A shows an enlarged view of a portion of the stent inaccordance with the first embodiment of the present invention;

[0026]FIG. 4 shows a cross-sectional view of the mold in accordance withthe first embodiment of the present invention;

[0027]FIG. 5 shows an isometric view of a mold in accordance with asecond embodiment of the present invention;

[0028]FIG. 6 shows a cross-sectional view of the mold in accordance withthe second embodiment of the present invention; and

[0029]FIG. 7 shows an isometric view of a stent in combination with anangioplasty balloon in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Although certain preferred embodiments of the present inventionwill be shown and described in detail, it should be understood thatvarious changes and modifications may be made without departing from thescope of the appended claims. The scope of the present invention will inno way be limited to the number of constituting components, thematerials thereof, the shapes thereof, the relative arrangement thereof,etc., and are disclosed simply as an example of the preferredembodiment.

[0031] Referring to FIG. 1, a stent 10 in accordance with the presentinvention is shown. The stent 10 is shown comprising multiple modular,wiring/filament sections 20. In the preferred embodiment, the stent 10is formed by a series of sections 20 of wire filaments that are endlesshoops or bands. However, the stent 10 may also be constructed by avariety of differently shaped filament sections. For instance, a seriesof lengths of filaments connected along their length (not shown) may beused. Alternatively, as shown in FIG. 2, a piece of filament, notsectional but rather a single length 25, that is looped in a generallyhelical fashion may be used. It is important to note that all of thesestructures are hereinafter referred to as “sections” 20 for conveniencesake only. Further, the illustration of the sections 20 in the form ofhoops is provided to more readily describe the present invention. Theuse of the term “sections” and the illustrations of hoops are chosen forconvenience of illustration and are in no way to be taken as limitingaspects of the claimed invention.

[0032] The sections 20 may be made of any material that is relativelystiff but with a high level of allowable plastic deformation. Thepreferred material is also biocompatible such that it is able towithstand the corrosive environment of the body. For example, tantalum,stainless steel, or a body-compatible mer such as polyethylene,polytetrafluoroethylene, and polyurethane have been used. The sections20 may also be made of a biodegradable polymer such as poly (L-lactide).It is also possible to provide the sections 20 with medicinal materialincorporated therein to aid in delivery of that material to neededareas. It is also possible to use a combination of the above notedmaterials, e.g., alternating sections 20 of metal and polymer.

[0033] Regardless of the form of the filament (e.g., sections such ashoops or lengths, or helical), the filament must be formed forconnection of the filament to itself or an adjacent section 20 such thata structure can be created that is longitudinally flexible for insertioninto the artery, yet radially stiff for good artery support. In thepreferred embodiment, the sections 20 are in a sinuous shape asillustrated in the drawings. The present invention should not, however,in any way be limited to the sinuous shape illustrated. For example, thesections may be shaped into: a square wave form, a repetitive peak form,etc. Further, the shape need not be identical from section to section oralong the length if a single length is chosen, i.e., the frequency ofthe shape chosen could shift integrally so as to allow for properalignment and a more dense matting of wire within the stent 10.

[0034] As illustrated in FIG. 1, the multiple sections 20 of thepreferred embodiment are assembled into a long continuous chain byconnecting all or selected crests 21 of one hoop/band to its neighboringhoop's/band's troughs 23. The points of connection being referred toherein as joints 30; the points of a non-connection being labeled 32.The material that forms the joint 30 between sections 20 should be shortto ensure axial rigidity. However, the shape of the joint 30 could bevaried according to designer requirements. For example, the joint 30could be shaped like a bar, flat strip, etc. Preferably polyethylene isused.

[0035] The joints 30 may be made of a variety of materials. Forinstance, the joints 30 may be the same material as the sections 20. Ina preferred embodiment of the present invention, however, the sections20 are made of a metal, e.g., tantalum or stainless steel, while thejoints are made of either a metal or a polymer. If a polymer is chosen,the polymer may be any body-compatible material usable in cardiovasculardevices such as polyethylene, polytetrafluoroethylene, polyurethane,etc.

[0036] As with the sections 20, the joints 30 could also be made frombiodegradable polymer such as poly(L-lactide). If made from thisbiodegradable material, a chain of metal wire band stents 10 could beinserted in the weak artery, become attached to the lining of the arteryin two weeks, and a joint 30 would disintegrate having performed aprimary function of forming temporary links during initial implantationinto the weak artery. As with the sections 20, the joints 30 could alsobe made of medicinal material to aid in delivery of medication to aneeded area.

[0037] The tooling to create the above described stent 10 is shown inFIGS. 3-6. In FIGS. 3 and 4, a first embodiment of the tooling for usewith injection molding processes is shown. The first embodiment includestooling 40 having a first part in the form of a fixture 41 including afirst upper portion 42 and a second lower portion 44, and a second partin the form of a mandrel 46. Each portion 42, 44 of the fixture 41includes a generally semicylindrical surface 43A and 43B, respectively,which when the portions 42, 44 are mated together form a generallycylindrical interior surface that dictates the shape of the stent 10. Itis important to note, however, that the cylindrical shape used herein isonly meant to be illustrative as other shapes could be used depending onthe particular body cavity in which the stent 10 is to be used. Forinstance, the shape could be polygonal or elliptical. The upper portion42 and lower portion 44 are aligned by guide pins 54.

[0038] As shown in FIGS. 3 and 3B, each area 43A, 43B includes grooves56 which are machined into the portions 42, 44 to accommodate thesections 20 of the stent 10. Alternatively, the grooves 56 could also bemachined to accommodate a single length of filament 25 if suchconstruction is desired. In any regard, the grooves 56 are positioned tolocate the filament, i.e., sections 20, in a desired location forconnection into a stent 10. Further, the grooves 56 will most often, butnot necessarily, be machined to hold the filament in the shape intowhich it was originally shaped, e.g., sinuous, thus allowing for ease ofinsertion of the wiring into the grooves 56.

[0039] In order to provide the joints 30 that connect the sections 20,joining openings 58 are machined into the grooves 56 as required. Thejoining openings 58 are positioned such that molten material injectedtherein will solidify around adjacent parts of the filament, e.g., thecrests 21 and neighboring troughs 23 of sections 20, so as to join themtogether. The joining openings 58 may be machined to provide any of thebefore mentioned shapes of joints 30.

[0040] Turning to the second part, the mandrel 46 generally includes abody 47 and base 49. The body 47 is generally shaped to closely matewith the internal surfaces 43A, 43B provided between the upper and lowerportions 42, 44 of the fixture, i.e., cylindrical. The base 49 tops themandrel and aids in proper alignment of the mandrel 46 within theinternal surfaces 43A, 43B via guide pins 48 in the portions 42, 44 andguide holes 50 in the base 49.

[0041] The mandrel 46 provides hot injection material to the joiningopenings 58 through a series of conduits in the mandrel. In particular,the conduits include an input 70 that enters the base 49 and runsthrough the center of the body 47, runners 74 which branch off of theinput 70, and gates 72 that connect the runners 74 to the joiningopenings 58. The alignment and close tolerances of the mandrel 46 andfixture inner surfaces 43A, 43B are critical parameters for a successfulset of tooling. The mandrel 46 should be made from insulating material,such as ceramic or phenolic, for safe operation. Water cooling may alsobe provided to the tooling 40 via conduits 62, if necessary.

[0042] As an alternative design, the tooling 40 is used as a mold forthe overall creation of the stent 10. In this application, the tooling40 would not receive previously constructed wiring/filament sections 20but rather would receive molten material through mandrel 46. The moltenmaterial would flow from the mandrel conduits 70, 72, 74 through thejoining openings 58 and into grooves 56 thus forming a one piece unitarystent 10 upon hardening. In this situation, it may be necessary to makecertain modifications in the tooling 40 that would accommodate morefluid flow. For instance, more runners 74 and gates 72 may be necessarywithin the mandrel 46.

[0043] The process of creating a stent 10 using the non-injectionmolding tooling is as follows. First, the wiring is shaped, e.g., into asinuous section 20. Second, the section 20 is placed within the grooves56. The placing of the sections 20 may occur in a variety of ways. Forinstance, one of the sections 20 may be placed in one of the portions42, 44 or the sections may be placed over the mandrel 46 and the mandrelpositioned over one of the portions 42, 44. Third, the tooling 40 isenclosed by coupling the missing part, i.e., portion 42, 44 or themandrel 46. Fourth, joints 30 are formed by the insertion of moltenmaterial into the mandrel 46 that flows to the joining openings 58 andsolidifies. Lastly, the tooling is opened and the completed stent 10 isremoved from the tooling 40 for use.

[0044] In the alternative that the tooling 40 is used as a completemold, the first two steps above are omitted. The tooling is connected,the molten material is injected and the completed stent 10 is removedfrom the tooling once the material is hardened.

[0045] Referring to FIGS. 5 and 6, a second embodiment of the tooling inaccordance with the present invention is shown. This tooling allows foruniform, one time welding of stent sections 120. The one time welding isprovided by a laser and fiber optic system 180.

[0046] The second embodiment is similar in structure to that of thefirst embodiment in that the tooling 140 includes a first part having afirst upper portion 142 and a lower second portion 144. The portions142, 144 each have a generally semicylindrical surface 143A, 143B whichjoin to form a generally cylindrical interior surface. A mandrel 146 isprovided to support the sections 120 within the tooling 140. Again, itis important to note that the shape of the surfaces 143A, 143B andmandrel 146 may be varied, e.g., polygonal or elliptical.

[0047] In this embodiment, however, the mandrel does not have conduitstherein. Here, the portions 142, 144 are provided with a plurality offiber optic channels 190 that open onto the grooves 156 at desired jointpositions, e.g., where filaments of neighboring sections 120 areadjacent one another. Within each channel 190, a fiber optic lens 188 ispositioned. The lenses 188 are connected via fiber optic lines 184 to aheating source 181, e.g., a laser. The laser heating source 181 is asource of welding heat that is transmitted along the fiber optic lines184 and focused by lenses 188 on the selected points of the sections120.

[0048] With the present invention, the repetitive heating and cooling ofthe sections 120 during welding is reduced in that all of the joints 30,130 are created in a single step, i.e., a material injection or a singletransmission from a heating source 181 to lenses 188. As a result, themanufacturing process is quicker and more reliable using the presentinvention because of the substantially simultaneous creation of thejoints 30, 130. Furthermore, the tooling 40, 140 allows for moreconsistent alignment of the joints 30, 130 because the sections 20, 120are held in their desired position. The stent created, therefore, hasmaximum flexibility for insertion with maximum rigidity for artery wallsupport.

[0049]FIG. 6 shows a stent 210 in combination with an angioplastyballoon 294. The device is shown in an intermediate step of use in whichan angioplasty balloon 294 is enlarged within the stent 210. The stent210 may take the form of any of the above-identified stent embodiments,e.g., filaments formed of a first material and the joints 230 of asecond material. In use, the angioplasty balloon 294 and stent 210 areused together to position the stent 210 within an artery of a body. Inparticular, the stent 210 is collapsed around the balloon 294 and thenpositioned within a body artery where the balloon 294 is expanded toextend the stent 210 to an in-use position. Accordingly, the presentinvention also includes the angioplasty balloon 294 and stent 210 incombination.

[0050] While this invention has been described in conjunction with thespecific embodiments outlined above, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the preferred embodiments of theinvention as set forth above are intended to be illustrative, notlimiting. Various changes may be made without departing from the spiritand scope of the invention as defined in the following claims.

I/We claim:
 1. A stent comprising: at least one filament made of a firstmaterial; and joints made of a second material connecting selectedfilaments to one another.
 2. The stent of claim 1 , wherein at least oneof the first material and second material includes medicine.
 3. Thestent of claim 1 , wherein at least one of the first and second materialis biodegradable.
 4. The stent of claim 1 , wherein the first materialis one of a metal and a polymer.
 5. The stent of claim 4 , wherein thefirst material is selected from the group consisting of: tantalum,stainless steel, polyethylene, polytetrafluoroethylene, polyurethane,and poly (L-lactide).
 6. The stent of claim 1 , wherein the at least onefilament includes at least two filaments made of differing firstmaterials, the first materials being chosen from metal and polymer. 7.The stent of claim 6 , wherein the first material is selected from thegroup consisting of: tantalum, stainless steel, polyethylene,polytetrafluoroethylene, polyurethane, and poly (L-lactide).
 8. Thestent of claim 1 , wherein the second material is one of a biodegradablepolymer, a non-biodegradable polymer, a medicinal material and a metal.9. The stent of claim 8 , wherein the second material is selected fromthe group consisting of: tantalum, stainless steel, polyethylene,polytetrafluoroethylene, polyurethane, and poly (L-lactide).
 10. Incombination: an angioplasty balloon; and a stent, including at least onefilament made of a first material and joints made of a second material,adapted for use with the angioplasty balloon.
 11. The stent of claim 10, wherein at least one of the first and second material includesmedicine.
 12. The stent of claim 10 , wherein at least one of the firstand second material is biodegradable.
 13. The stent of claim 10 ,wherein the at least one first material is one of a metal and a polymer.14. The stent of claim 13 , wherein the first material is selected fromthe group consisting of: tantalum, stainless steel, polyethylene,polytetrafluoroethylene, polyurethane, and poly (L-lactide).
 15. Thestent of claim 10 , wherein the at least one filament includes at leasttwo filaments, the at least two filaments being made of differing firstmaterials chosen from metal and polymer.
 16. The stent of claim 15 ,wherein the first material is selected from the group consisting of:tantalum, stainless steel, polyethylene, polytetrafluoroethylene,polyurethane, and poly (L-lactide).
 17. The stent of claim 10 , whereinthe second material is one of a biodegradable polymer, anon-biodegradable polymer, a medicinal material and a metal.
 18. Thestent of claim 17 , wherein the second material is selected from thegroup consisting of: tantalum, stainless steel, polyethylene,polytetrafluoroethylene, polyurethane, and poly (L-lactide).
 19. Toolingfor forming a stent comprising: a first part including grooves foraligning filaments.
 20. The tooling of claim 19 , further comprising asecond part including conduits for directing joint forming material toselected positions of the first part whereby joints are formed betweenfilaments.
 21. The tooling of claim 19 , wherein the first part includesa first portion and a second portion, wherein the first portion andsecond portion mate to form a generally cylindrical internal surface.22. The tooling of claim 21 , wherein the grooves are formed along thegenerally cylindrical internal surface.
 23. The tooling of claim 22 ,further comprising a second part including conduits for directing jointforming material to selected positions of the first part whereby jointsare formed between filaments.
 24. The tooling of claim 23 , wherein thesecond part is a mandrel that fits within the generally cylindricalsurface.
 25. The tooling of claim 23 , wherein the first part includesenlarged openings in the grooves to accommodate creation of jointsbetween the filaments, and wherein the conduits of the second partdeliver the joint forming material to the openings.
 26. A tooling forforming a stent comprising: means for positioning filaments; and meansfor joining filaments.
 27. The tooling of claim 26 , wherein the meansfor positioning filaments includes a first part including grooves toposition the filaments and a second part including conduits fordirecting joint forming material to selected positions of the first partwhereby joints are formed between filaments.
 28. The tooling of claim 27, wherein the first part includes a first portion and a second portion,wherein the first portion and second portion mate to form a generallycylindrical internal surface.
 29. The tooling of claim 28 , wherein thegrooves are formed along the generally cylindrical internal surface. 30.The tooling of claim 28 , wherein the second part is a mandrel that fitswithin the generally cylindrical surface.
 31. The tooling of claim 27 ,wherein the first part includes enlarged openings in the grooves toaccommodate creation of joints between the filaments, and wherein theconduits of the second part deliver the joint forming material to theopenings.
 32. A method of making a stent, the method comprising thesteps of: providing a fixture having internal grooves; placing filamentsinto the grooves; and joining the filaments together.
 33. The method ofclaim 32 , wherein the step of providing a fixture having internalgrooves includes providing the grooves in a generally cylindrical shape.34. The method of claim 32 , wherein the step of joining the filamentsincludes simultaneously welding selected adjacent filaments with a laserheating source.
 35. The method of claim 32 , wherein the step of joiningthe filaments includes injecting a molten material to form jointsbetween the filaments.
 36. The method of claim 32 , wherein the step ofproviding a fixture includes providing a mold with a generallycylindrical interior surface including the grooves and a mandrel havingconduits to deliver joint forming material to the grooves.
 37. Themethod of claim 36 , wherein the grooves include openings to receive thejoint forming material.
 38. The method of claim 32 , wherein the step ofplacing the filaments into the grooves includes placing the filamentssuch that portions of the filaments are proximate one another.
 39. Amethod of fabricating a stent comprising the steps of: providing a moldhaving internal grooves; and injecting a material into the mold to fillthe grooves.
 40. The method of claim 39 , wherein the material is amolten material.